1. Field of the Invention
This invention pertains to infinite-ratio driving connections between two or more interlocked drums. More specifically, it pertains to an improved interlock drive and slack-pulling arrangement for a log yarding system.
2. Description of the Prior Art
Most logging yarders employ at least a main drum and a haulback drum with corresponding wire ropes wrapped on the drums. The function of these drums is to spool back and forth the main and haulback lines of a log-hauling cable. As is well known, the lines are strung between the yarder and tail-block located at the extreme outer limit of the area being logged. A choker or grapple is attached to the main line. When the carriage is being hauled out or hauled in, it is necessary to pay out one of the lines as the other is being spooled in and to maintain the same speed when wraps on the drums change to affect the speed so as to maintain the lines sufficiently taut such that the logs are not dragged along the ground.
When the chokers or grapple are positioned over the logs, relative movement is necessary between the drums to allow the grapple or choker lines to be dropped down to the logs. Thus it is also necessary in a yarder that the haulback and main drums to be operated at different speeds relative to one another.
Interlock mechanisms between the two drums have been used heretofore to enable the two drums to run at correlated relative speeds of rotation through planetary gear systems. Typical examples of these types of yarders are described in U.S. Pat. Nos. 3,405,878 and 3,733,812. Basically, the prior systems, however, are expensive to manufacture and thus too costly to use in lower priced, smaller capacity yarders.
Grapple operation requires that the yarder provide a means of lowering, opening and closing the grapple. For this purpose, a slack-pulling drum with a corresponding slack-pulling line is provided, and the yarder system is called a three-drum or three-line yarder. Similarly, in other three-line yarders, a slack-pulling line is provided to extend and retract choker cables. All known three-line yarders require brakes and clutches to effectively operate the third slack-pulling drum. Elimination of these components simplifies the operation of the yarder unit and reduces the manufacturing expense.